Evidence for Polarity- and Viscosity-Controlled Pathways in the Termination Reaction in the Radical Polymerization of Acrylonitrile
Evidence for Polarity- and Viscosity-Controlled Pathways in the Termination Reaction in the Radical Polymerization of Acrylonitrile
复制标题
丙烯腈自由基聚合终止反应中极性和粘度控制途径的证据
DOI：
10.1021/acs.macromol.1c00158
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发表时间：
2021
期刊：
影响因子：
5.5
通讯作者：
Yamago Shigeru
中科院分区：
文献类型：
--
作者：
Li Xiaopei;Ogihara Tasuku;Kato Tatsuhisa;Nakamura Yasuyuki;Yamago Shigeru
通过对聚丙烯腈（PAN）链端自由基1a和PAN末端模拟小模型自由基1b反应产物的分析，确定了丙烯腈（AN）自由基聚合的终止机理。三个竞争机制的贡献，即，明确地确定了反硝化（Disp）、通过碳-碳形成的结合（CC-Comb）和通过碳-氮键形成的结合（CN-Comb），其中CN-Comb是首次通过实验鉴定的。Disp和CC-Comb之间的选择性表现出良好的相关性与反应体系的粘度和温度，和Disp的选择性增加的粘度增加，如先前报道的其他单体的终止。相比之下，CN-Comb对粘度不敏感，但对介质的极性敏感; CN-Comb在极性介质中受到抑制。这些结果强烈表明存在两种途径的终止反应，即极性和粘度控制的途径。CN-Comb产物5在聚合过程中是稳定的，但在高温下分解成Disp和CC-Comb产物。因此，在PAN加工（如熔融成型）中必须小心，因为Disp和CC-Comb组成的变化会影响PAN基材料的物理性能。
The termination mechanism in the radical polymerization of acrylonitrile (AN) was determined through the product analysis for the reaction of structurally well-defined polyacrylonitrile (PAN) chain-end radical1aand PAN-end mimetic small model radical1b. The contributions of three competing mechanisms, i.e., the disproportionation (Disp), the combination by carbon–carbon formation (CC-Comb), and the combination by carbon–nitrogen bond formation (CN-Comb), were unambiguously determined, with CN-Comb being identified experimentally for the first time. The selectivity between Disp and CC-Comb showed a good correlation with the viscosity and temperature of the reaction system, and the Disp selectivity increased as the viscosity increased, as previously reported for the termination of other monomers. In contrast, CN-Comb is insensitive to the viscosity but sensitive to a polarity of media; CN-Comb is suppressed in polar media. These results strongly suggest the presence of two pathways in the termination reaction, namely, the polarity- and viscosity-controlled pathways. The CN-Comb product5was stable during the polymerization but decomposed into Disp and CC-Comb products at high temperatures. Therefore, care must be taken in PAN processing, such as the melt molding, as changes in Disp and CC-Comb composition can affect the physical properties of PAN-based materials.